Distribution of the SOID values in G2 and mitotic cells treated with ATM or CHK1/2 inhibitor. Exponentially-growing normal human primary fibroblasts were irradiated with 0.4 Gy of X-rays in the presence of KU55933 (A - D) or SB218078 (E - H). Two hours later, cells were fixed and subjected to immunofluorescence staining for Ser139-phosphorylated H2AX and Ser10-phosphorylated H3. The SOID values of phosphorylated H2AX foci in the control cells (A, C, E and G) and 0.4 Gy-irradiated cells (B, D, F and H) were measured. G2 cells (A, B, E and F) and mitotic cells (C, D, G and H) were identified as described in Figure 2. Dotted lines indicate 4000 SOID, and the numbers indicate the percentage of cells with the SOID above 4000.